This invention relates generally to valve seals and more particularly to a seal construction suitable for use in a valve or the like which is subjected to elevated service temperatures and vibration.
The valve seal of the present invention finds particular utility in conjunction with valves which are subjected to vibration and high temperatures. In use such valves, for example, may be used to control the direction of flow of the exhaust gases from diesel-powered engines of the type commonly used to power gas pumping stations and compressor stations. In use, these large, reciprocating engines emit a high temperature exhaust gas and, likewise, transmit a relatively high vibration level to the downstream, exhaust duct work. In light of ongoing activities to further conserve energy, many industrial users of such equipment have taken steps to install heat recovery units in an effort to capture some of the waste heat carried off by the exhaust gases emitting therefrom. In such installations which utilize such heat recovery systems, it is desirable to divert some or all of the exhaust gases emanating from the engine to the heat recovery system by way of appropriate valves in the exhaust duct work. The valve system diverts a portion of the exhaust gases to the heat recovery system or to the exhaust muffler system. In the event the heat recovery system requires maintenance due to breakdown or the like, the valve system is completely closed in order to isolate the heat recovery system from the hot exhaust gases so as to provide a safe environment for the workers performing the maintenance thereon.
Due to the high temperatures and relatively high operating vibrational levels encountered in the exhaust duct work of these engines, it has heretofore been common practice to employ large and expensive valves to control the exhaust gases. These known valves may be of a wide variety of constructions and designs, such as a butterfly valve or a gate valve which employs a heavy sliding metal blade which makes metal to metal contact with the valve seat in order to minimize gas leakage in the closed position. In other words, these commonly used valves do not employ gaskets or other attached sealing strips but rely solely upon the metal to metal contact between the blade and valve seat to achieve a seal.
Such a gasket or sealing strips when used in such an environment must be capable of withstanding vibration and high temperatures and have a high degree of resiliency.
It is generally known in the art of constructing packing or sealing strips to provide a sealing member having a core which contains a soft or resilient material so as to maintain sealing engagement between the mating surfaces to be sealed and which will maintain its resilience under pressure or prevent permanent deformation of the core. For example, U.S. Pat. No. 2,144,082 discloses a composite core of both soft and firm rubber for sealing an automobile door.
When encountering higher service temperatures, the desirability of employing materials which will retain their mechanical properties, such as tensile strength and resiliency at elevated service temperatures. has also been recognized. For example, U.S. Pat. No. 2,882,082 discloses a fire resistant gasket constructed of strips of knitted metal mesh fabric and metal foil suitable for use in the fire walls of jet engine aircraft.
Combinations of high temperature materials have also been utilized. In U.S. Pat. No. 3,578,764, a gasket construction for sealing the door of a self-cleaning oven is disclosed having a tubular metal mesh core sheathed by a tubular knit fiberglass fabric which is said to be suitable in temperatures in excess of 900.degree. F.
Of course, the above-mentioned seals are not intended to be subjected to the vibration and abrasion caused by hot exhaust gases and it is doubtful that any of them could function satisfactorily in such an environment for any period of time.
Since a substantial amount of vibration is transmitted to the valve, it is desirable to provide a seal that can withstand that vibration. This is an important requirement since the vibration abrades known sealing material and degrades known seals after a period of time.
In such service conditions it is also desirable to provide a seal which is capable of withstanding high temperatures. In such high temperatures, known seals are subject to degradation. As such a valve seal degrades, it loses its effectiveness and permits substantial leakage through the valve.
It is also desirable that such a seal have a high degree of resiliency, that is, the capability of returning to its original state after compression thereof. When a valve is moved to a closed position and the sealing material is compressed, its sealing effectiveness increases and minimizes the amount of leakage through the valve. When the valve is subjected to a substantial amount of vibration, there is a certain amount of "fluttering" that may occur as a result of the pulsating pressure. When the valve is provided with a seal having a high degree of resiliency, a sealing relationship is maintained between the valve body and the valve blade since the sealing material stays in contact with both of the valve members even though some slight movement may occur therebetween. It should be further understood that this "fluttering" further acts to abrade the sealing material and degrade it as described herein.
In dealing with the high temperatures and high vibration levels encountered in the exhaust duct work of diesel-powered pumps and compressors and the like, the prior art has failed to develop or suggest a seal construction which can successfully withstand this severe service environment without early degradation and failure. It has been found that the seal construction of the present invention exhibits superior sealing characteristics over known high temperature seals without degradation due to abrasion and vibration.